The invention relates generally to ion implanters for the processing of semiconductor wafers, and more particularly to wafer support pedestals and wafer cooling systems for ion implanters.
Ion implanters are used to introduce conductivity-altering impurities into semiconductor wafers. In order to accomplish this, the desired impurity material is ionized via an ion source, and then accelerated to form an ion beam of prescribed energy. The ion beam is then directed at the surface of the semiconductor wafer so that the ions in the beam penetrate the semiconductor material and are embedded in the crystalline lattice thereby forming a region of desired conductivity.
In semiconductor wafer processing, there are several important considerations in achieving an effective ion implanter. One important factor is throughput, or the number of wafers processed per time unit. In addition, wafer transfer time, ion implant time and implanter down time are other important considerations. Another important factor is the ability to implant at high angle tilt. A high tilt angle, generally in the range of about 20 to about 60 degrees, allows doping of the silicon structure beneath an obstruction to the beam. Another important consideration is the ability to cool the wafers during processing.
Serial implanters process silicon wafers one at a time. Batch implanters process a plurality, or batch, of wafers simultaneously. Typical batch ion implanters utilize a rotating disk upon which wafers to be processed are mounted on pedestals. In batch implantation systems, it is important to be able to tilt and cool the wafers without resulting in an unbalanced rotating condition. This condition can occur, for example, when all of the pedestals do not move into position at the same time resulting in the coolant creating an unbalanced load. Thus, an ion implanter system capable of high wafer throughput, uniform dose with the capability of high tilt angle implantation and wafer cooling is desired.
The invention provides in one aspect a wafer platform including at least one wafer pad assembly for mounting and cooling a wafer and being disposed in an ion implanter. The wafer pad assembly comprises a wafer support pad having an upper surface for mounting the wafer and a lower surface. The lower surface of the wafer support pad is connected to a coolant passage having an inlet section and an outlet section arranged in an opposed configuration, wherein the mass of the inlet section is counterbalanced by the mass of the outlet section.
The invention provides in another aspect a wafer pad assembly for mounting a wafer and being disposed in an ion implanter. The wafer pad assembly comprises a wafer support pad having an upper surface for mounting the wafer and a lower surface for mounting one or more coolant passages. The lower surface is connected to a frame having an outer curved surface in mating engagement with a complementary shaped bearing surface of a housing wherein the wafer can be rotated about the axis of the centerline of the wafer mounted on the pad.
These and other aspects and advantages of the present invention will be readily understood and appreciated by those skilled in the art from the following detailed description of the preferred embodiments with the best mode contemplated for practicing the invention in view of the accompanying drawings.